Variable grid leak



Feb. 5, 1927.

J. J. GHEGAN VARIABLE GRID LEAK Filed April 13, 1923 IIIIIIIIIIIIIIIIIIIIIIII) V I Ill! ' IINVENTOR 3 M ATTORNEY 'Patented Feb. 15, 1927.

UNITED STATES JOHN J. GHEGAN, OF EAST ORANGE, NEW JERSEY.

VARIABLE GRID LEAK.

Application filed April 13, 1923.

Some of the more important objects of this invention are to provide a grid leak of simple and inexpensive construction and which can be quickly and easily adjusted to obtain desired effects.

It has been known for some time that a pencil mark between terminals would answer the purpose of high resistance shunt path necessary for a grid leak. My invention involves the utilization of this'knowledge and the provision of means for providing a pencil line resistance in a practical, usable form.

Other features of the invention will ap pear as the specification proceeds and particularly as the same is read in conjunction with the accompanying drawing which forms a part of the same.

In the drawing referred to I have illustrated but one commercial form of the invention, and therefore wish it understood that structural changes may be made without departing from the broad spirit and scope of the invention as hereinafter defined and claimed.

2 Figure 1 is a top plan view of a present form of the invention as it appears with the cover removed.

Figure 2- is a cross sectional view as on substantially the plane of line 22 of Figure 1 with the cover in'place but partly broken away and shown in section.

Figure 3 is an enlarged broken sectional view of the adjustable lead carrier.

Figure 4- is a fragmentary part sectional 3 view as on substantially the plane of line l4'of Figure 1.

' In the form of the invention illustrated, there is a substantially circular base 5 of suitable insulating material, forming a support at the center of which there is pivoted at 6 a swinging arm 7 having an insulating handle 8 and carrying a socket 9 in which there is slidingly engaged avstick of graphitic material or pencil point 10 disposed to track over the face of the insulating base. This socket may be inexpensively provided in the end of the lever arm, as shown in Figure 3, by providing a tubular stud l1 riveted or otherwise suitably secured in the end of the lever as shown at 12, and having a reduced stem part 13 over which the insulating handle may be engaged.

As the lever is shifted about its pivot, the graphite will rub off and leave a conducting track or path 14 on the face of the support, the length of which will depend on the Serial No. 631,816.

position of the lever. By swinging the lever back and forth a number of times the density of this conducting path may be increased, as suggested in Figure 1, where it will be seen that the left hand section of the track is heavier than the right hand portion thereof. If desired, at any time the entire track may be removed by simply rubbing it off as by means of an ordinary pencil eraser, after which. an entirely new path may be made by'simply swinging the lever as far as may be desired and either one or a number of times.

To assure uniform results the graphite marker is preferably backed up by a light spiral spring seated in the end of the holder, as shown at 15 in Figure 3.

At one end of the movement of the lead carrier a suitable terminal is provided, such as the plate shown at its end inclined down into a cavity 17 in the base so as to bring its upper face down to the plane of the support. With this construction the point of the graphite rides from the fiat surface of the support up on to the inclined face of the terminal so as to make firm contact with the latter and the extent of this movement may be governed by a stop pin 18 which is shown as extended down through'the plate into the base to aid in positioning the plate on the base. To prevent any gap or loss of contact at the junction of the metal terminal with the base, a coating of india ink or other conducting material may be applied over the meeting edges of the plate and base, as indicated at 19.

The terminal plate is shown provided with a suitable binding post 20 for connecting the same in circuit and another binding post 21 is shown mounted on the base adtravel and final 16 in Figure 1, having jacent the first for connecting the adjusting arm in circuit by way of a connection 22 extending from said binding post to the pivot stud of the arm. A second stop pin is shown provided at 23 for limiting the swinging movement the terminal plate and this stop is preferably positioned as shown so as to allow for a full swing of the lever, that is, throughout an arc involving the greater part of the circular base.

To protect the parts from dust and moisture and to provide a guard for preventing accidental shifting of the adjusting arm, a cover-may be engaged over the base such of the lever away from as shown at 24, said cover being illustrated as slipped down over a reduced shouldered portion 25 of the base and detachably held by a pin 26 on the base engaging in a bayonet slot 27 in the rim of the cover.

The invention, it will be seen, provides in simple and inexpensive form,fa means whereby a grid leak of practically any desired resistance may be created and varied continuously, throughout N a considerable range. Also, the resistance path is both removable and renewable sothat the invention is adaptable to efle'ct practically all the results required of adevice of this character. The pivot post for the adjustable arm is desirably in the form of a screw such as illustrated, which may be tightened to increase the tension on the arm for holding it frictionally in any desired osition of adjustment. The base being 0 insulating material presents a fairly rough surface to the graphite and this is desirable as it causes the graphite to rub off readily and leave an appreciable mark for the resistance path.

As the inventionis of broad scope it will be understood that the terms which have been employed herein are; used in a descriptive rather than in a limiting sense, except for such limitations as may be imposed by the prior-art. 7

What I claim is: f 1. A variable grid leak comprising an insulating support, a terminal on the support having a contact face inclined to meet the surface of the support and a conductive marker mounted for movement over the support and up the inclined face of the terminal, said movable marker having a stationary terminal on thesupport. I 2. A variable grid leak comprising an insulating support having a depression in the face thereof,a terminal mounted on the support and having an inclined portion extending into said depression and an electrically conductive marker mounted for travel over the support and onto said inclined portion of the terminal.

3. In a device of the character disclosed, an insulating base, an electrically conductive marker mounted for travel over said base, a terminal on the base having an inclined surface for the marker to ride over, a terminal for the marker, on the base, spring means for holding the marker engaged with the base and inclined surface of the terminal, a-handle for shifting the marker, a cover forming a housing for the marker and handle, said cover having a close-fitting engagement with the base and means for detachably securing the cover this engaged with the base.

In witness whereof, I have hereunto set my hand this 9th day of April, 1923.

JOHN J. GHEGAN. 

